Multi-carrier transmission method and data transmitter

ABSTRACT

Equipped with a plurality of mapping blocks  102  and  103  that carry out mappings of different rates, signals subjected to low-speed mapping are placed in the periphery of a band to which a plurality of sub-carriers are assigned at an interval corresponding to the symbol rate. The signal placed on the frequency axis in this way is converted to a time waveform through inverse Fourier transformation block  105,  converted to a symbol time series through parallel/serial conversion block  106,  then quadrature-modulated and transmitted.

TECHNICAL FIELD

The present invention relates to a multi-carrier transmission method,data transmission apparatus using this method, and mobile station andbase station apparatuses incorporating this data transmission apparatus.

BACKGROUND ART

In mobile communications, there is a strong demand for multi-path fadingcountermeasures and improvement of the transmission quality. Multi-pathfading can be overcome by reducing the symbol rate. On the other hand,implementing high-speed data transmission requires multi-carriertransmission. The best way to narrow sub-carrier intervals inmulti-carrier transmission is the OFDM system. Conventional datatransmission apparatuses using the OFDM system prevent leakage ofunnecessary signals to outside a band by inserting null symbols at bothends of the band or placing restrictions on the band.

FIG. 1 is a block diagram showing the configuration of a datatransmission apparatus using the OFDM system. In the data transmissionapparatus shown in said figure, transmission data 1 is mapped by mappingblock 2. For example, in the case of QPSK, mapping is carried out on 4types of phase, 2 bits at a time, and in the case of ASK, mapping iscarried out on 2 types of amplitude, one amplitude bit at a time. Themapped signal is serial/parallel-converted in serial/parallel conversionblock 4 and then subjected to inverse Fourier transformation (IFFT)together with null symbol 3 in inverse Fourier conversion block 5.Through this processing, the signal placed on the frequency axis isconverted to a time waveform.

FIG. 2 is a drawing showing the spectrum of a single sub-carriercentered on frequency f0. FIG. 3 shows these spectra lined up on thefrequency axis. In this example, signals are carried on fivesub-carriers and no signal is transmitted on 4 bands on each of theright and left sides. This band area where no signal is transmitted iscalled “guard frequency band,” which is implemented by means of nullsymbol 3.

The inverse-Fourier-transformed signal by inverse Fourier transformationblock 5 is modulated through parallel/serial conversion inparallel/serial conversion block 6 to a time-series signal and furtherquadrature-modulated in quadrature modulation block 7 to a radiofrequency signal and transmitted from transmission antenna 8. Thus,providing the guard frequency band where no signal is transmitted bymeans of null symbol 3 prevents leakage of unnecessary signal componentsto outside the band.

However, the data transmission apparatus above requires a lot of nullsymbols, which results in inconvenience such that the frequencyutilization efficiency is reduced when carrying out frequency divisionespecially on the uplink and that it is more vulnerable to distortion bymulti-paths, etc.

FIG. 4 is a block diagram showing the configuration of a datatransmission apparatus reinforced by guard intervals against distortionby multi-paths. In the data transmission apparatus shown in said figure,transmission data 1 is mapped by mapping block 2 and the mapped signalis serial/parallel-converted in serial/parallel conversion block 4, thensubjected to inverse Fourier transformation together with null symbol 3in inverse Fourier transformation block 5, and the signal placed on thefrequency axis is transformed to a time waveform. Theinverse-Fourier-transformed signal is converted to a time-series signalthrough parallel/serial conversion by parallel/serial conversion block6. Then, guard intervals are inserted into this signal in guard intervalinsertion block 9.

As shown in FIG. 5, the guard interval is the last part of a validsymbol period added to the start of the symbol. This prevents distortioneven if a delay wave lasting shorter than the guard interval may exist,making the signal resistant to multi-paths.

The signal with the guard interval inserted is quadrature-modulated inquadrature modulation block 7, converted to a radio frequency signal andtransmitted from transmission antenna 8. Thus, inserting the guardinterval makes the signal resistant to multi-paths.

However, the data transmission apparatus described above has a defect ofits transmission efficiency being reduced due to the guard intervalinserted to make the signal resistant to multi-paths, requiring a lot ofnull symbols. This results in a reduction of the frequency utilizationefficiency especially when carrying out frequency division on theuplink.

FIG. 6 is a block diagram showing the configuration of a datatransmission apparatus with the frequency utilization efficiencyimproved by narrowing the guard frequency through band restrictions. Inthe data transmission apparatus shown in said figure, transmission data1 is mapped by mapping block 2 and the mapped signal isserial/parallel-converted in serial/parallel conversion block 4, thensubjected to IFFT in inverse Fourier transformation block 5. The signalsubjected to IFFT is parallel/serial-converted in parallel/serialconversion block 6 to a time-series signal and guard intervals areinserted into it in guard interval insertion block 9. The signal withthe guard interval inserted is subjected to band restrictions in bandrestriction block 10 with the guard frequency band narrowed, thenquadrature-modulated in quadrature modulation block 7 to a radiofrequency signal and transmitted from transmission antenna 8.

In this case, in order to absorb distortion due to the band restrictionsby band restriction block 10, providing guard intervals with a lengthcorresponding to the impulse response length of a band restrictionfilter can remove distortion due to the band restrictions. Thus, bandrestrictions through band restriction block 10 can narrow the guardfrequency part and improve the frequency utilization efficiency withoutnull symbol insertion, etc.

However, the data transmission apparatus described above has a defect ofits time efficiency being reduced because it requires extra guardintervals corresponding to the length of impulse response of the filterused for band restrictions.

FIG. 7 is a block diagram showing the configuration of a datatransmission apparatus that disperses load between a guard frequency andguard interval. In the data transmission apparatus shown in said figure,transmission data 1 is mapped by mapping block 2 and the mapped signalis serial/parallel-converted in serial/parallel conversion block 4, thensubjected to inverse Fourier transformation together with null symbol 3in inverse Fourier transformation block 5. The signal subjected to IFFTin inverse Fourier transformation block 5 is parallel/serial-convertedin parallel/serial conversion block 6 to a time-series signal and guardintervals are inserted into it in guard interval insertion block 9. Thissignal is subjected to band restrictions in band restriction block 10with its guard frequency reduced, then quadrature-modulated inquadrature modulation block 7 to a radio frequency signal andtransmitted from transmission antenna 8. Thus, carrying out bothinsertion of null symbol 3 and band restrictions makes it possible toreduce the number of null symbols compared to the case where only nullsymbol 303 is inserted and reduce the length of guard intervals toabsorb distortion due to filtering compared to the case where only bandrestrictions are applied.

However, although this apparatus disperses load between the guardfrequency and guard interval, it has the disadvantage of both thefrequency utilization efficiency and time efficiency being reduced.

Thus, the conventional data transmission apparatus has problems thatrequire solutions such as reducing the frequency utilization efficiencybecause it requires a lot of null symbols, being vulnerable todistortion by multi-paths because it has no guard interval, reducing thetransmission efficiency due to the guard interval, reducing the timeefficiency due to extra guard intervals, etc.

DISCLOSURE OF INVENTION

It is an objective of the present invention to provide a datatransmission apparatus capable of improving the frequency utilizationefficiency at both ends of a band, resistant to multi-paths because ofits ability to introduce guard intervals, and capable of securing boththe frequency utilization efficiency and time utilization efficiency byintroducing band restrictions.

This objective is achieved by a multi-carrier transmission method thatsets the distance between sub-carriers so that they may be orthogonal toone another, assigns a plurality of sub-carriers to a specific band andassigns low-speed variable signals to the guard frequency parts set atboth ends of the specific band.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a functional block diagram of a conventional data transmissionapparatus that inserts null symbols;

FIG. 2 is a spectral map of a single carrier;

FIG. 3 is a spectral map of sub-carriers forming. multi-carriers;

FIG. 4 is a functional block diagram of a conventional data transmissionapparatus that inserts guard intervals;

FIG. 5 is a conceptual drawing showing how to insert guard intervals;

FIG. 6 is a functional block diagram of a conventional data transmissionapparatus that applies band restrictions;

FIG. 7 is a functional block diagram of a conventional data transmissionapparatus that disperses load between a guard frequency and guardinterval;

FIG. 8 is a functional block diagram of the conventional datatransmission apparatus that relates to Embodiment 1 of the presentinvention;

FIG. 9 is a spectral map of a single carrier;

FIG. 10 is a spectral map showing the signal layout of the datatransmission apparatus in Embodiment 1;

FIG. 11 is a functional block diagram of the data transmission apparatusthat relates to Embodiment 2 of the present invention;

FIG. 12 is a spectral map of a single carrier when guard intervals areinserted;

FIG. 13 is a spectral map showing the signal layout in the datatransmission apparatus in Embodiment 2; and

FIG. 14 is a functional block diagram of the data transmission apparatusthat relates to Embodiment 3 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention is a multi-carriertransmission method that sets the distance between sub-carriers so thatthey may be orthogonal to one another, assigns a plurality ofsub-carriers to a specific band, and assigns low-speed variable signalsto the guard frequency parts set at both ends of the specific band. Thismakes it possible to use bands that have not been available as guardfrequencies.

In this method, it is desirable to convert a signal placed on thefrequency axis of a specific band to a symbol time series and insertguard intervals between those symbols. This makes it possible to improvethe resistance to multi-paths.

In this method, it is also desirable to have a continuous phase over aplurality of symbols for a low-speed variable signal which remains thesame over a plurality of symbols according to the amount of phase changebetween guard intervals. In this way, even if guard intervals areinserted, the phase becomes continuous at a stage at which guardintervals are inserted.

In this method, it is desirable to apply band restrictions only to anarea of unnecessary signals that can be eliminated through a filter witha short impulse response. This makes it possible to reduce leakage ofsignals to outside the band without extending guard intervals.

A second embodiment of the present invention is a multi-carriertransmission method using the OFDM system that places a low-speedvariable signal instead of inserting null symbols at both ends of theband. This makes it possible to use bands which have not been availableas guard frequencies.

A third embodiment of the present invention is a data transmissionapparatus, comprising a plurality of mapping blocks that carry outmappings with different rates, a section that places signals subjectedto low-speed mapping around a band to which a plurality of sub-carriersare assigned at an interval according to the symbol rate, and a sectionthat converts a signal placed on the frequency axis of said band to asymbol time series. This configuration makes it possible to use bandswhich have not been available as guard frequencies, improving thefrequency utilization efficiency and increasing the number of data thatcan be transmitted.

In this data transmission apparatus, it is desirable to provide a guardinterval insertion block that inserts guard intervals between symbolsand for the mapping block that carries out low-speed mapping to carryout mapping so that the phase of a low-speed signal may be continuousover a plurality of symbols according to the amount of phase changebetween guard intervals. This configuration makes the phase continuousat a stage at which guard intervals are inserted even if the signalremains the same over a plurality of symbols, making it also applicablewhen guard intervals are used.

Furthermore, in this data transmission apparatus, it is desirable toprovide a band restriction block to apply band restrictions only to anarea of unnecessary signals which can be eliminated through a filterwith a short impulse response. This configuration can achieve areduction of load on the filter and secure the frequency utilizationefficiency as well as time utilization efficiency simultaneously.

The multi-carrier transmission and data transmission apparatuses in thepresent invention are applicable to mobile station and base stationapparatuses in a radio communication system. This allows the frequencyutilization efficiency in the radio communication system to be improved.

With reference now to the attached drawings, the embodiments of thepresent invention are explained in detail.

(Embodiment 1)

FIG. 8 is a functional block diagram showing the configuration of thedata transmission apparatus in Embodiment 1 of the present invention. InEmbodiment 1, the data transmission apparatus using the OFDM system, oneof the multi-carrier transmission systems, is explained. That is, thedistance between sub-carriers is set to a fraction of the symbol rate sothat the sub-carriers may be orthogonal to one another, a number ofsub-carriers are assigned to a narrow band and guard frequencies are setby the spread portion of the spectrum of sub-carriers at both ends ofthe spectrum.

The data transmission apparatus in Embodiment 1 comprises high-speedmapping block 102 that maps transmission data 101 as high-speed symbolrate data by high-speed mapping 1, low-speed mapping block 103 that mapstransmission data 101 as low-speed symbol rate data by low-speed mapping2. Only the data mapped by high-speed mapping block 102 areserial/parallel-converted in serial/parallel conversion block 104. Theserial/parallel-converted data are input to inverse Fouriertransformation block 105 and the data mapped in low-speed mapping block103 are input to inverse Fourier transformation block 105 instead ofnull symbols. Inverse Fourier transformation block 105 subjects theserial/parallel-converted signal and low-speed mapped signal to inverseFourier transformation into a time-series signal. This time-seriessignal is quadrature-modulated in quadrature modulation block 107 to aradio frequency signal and transmitted from transmission antenna 108.

The operation of the data transmission apparatus configured as shownabove is explained. Transmission data 101 is divided into a plurality ofportions by rate and mapped at different speeds. In FIG. 8, there is adivision into mappings with 2 types of speed, however it may be dividedinto any number of types. The signal sent to high-speed mapping block102 is mapped as high-speed symbol rate data by high-speed mapping 1. Onthe other hand, the signal sent to low-speed mapping block 103 is mappedas low-speed symbol rate data by low-speed mapping 2. For example, thelow-speed rate is assumed to be ½ of the high-speed rate.

FIG. 9 is drawing showing the spectrum of a single sub-carrier ofsignals with different rates. In said figure, broken line 120 representsthe spectrum of a signal subjected to high-speed mapping, fine solidline 121 represents the spectrum of a signal with a rate ½ of the rateof signal 120 and bold solid line 122 represents the spectrum of asignal with a rate ¼ of the rate of signal 120.

In the present embodiment, if the sub-carriers of signals with differentrates as shown in FIG. 9 are lined up on the frequency axis, low-speedsignals are placed at both ends of a high-speed rate signal as shown inFIG. 10. In FIG. 10, fine solid line 130 represents a signal subjectedto high-speed mapping, solid line 131 represents the spectrum of asignal with a rate ½ of the rate of signal 130, solid line 132represents the spectrum of a signal with a rate ¼ of the rate of signal130, and solid line 133 represents the spectrum of a signal with a rate⅛ of the rate of signal 130.

The spectrum of highest-speed rate signal 120 becomes 0 at a frequencyobtained by multiplying the inverse number (FS) of the symbol rate by aninteger multiple. As seen from FIG. 9, if their mutual rates have arelationship of a power of 2, the spectra of other signals 121 and 122also become 0 on the frequency. That is, the signals having a mutualrelationship of a power of 2 are all orthogonal to the signal with thehighest rate. Using this fact, placing signals with a low-speed rate atboth ends of a signal with a high-speed rate allows signals to betransmitted effectively while maintaining their orthogonal relationship.

Then as described above, signal 131 with a rate ½ of that of thehigh-speed rate signal is placed at the position of two carrierfrequencies next to high-speed rate signal 130, signal 132 with a rate ¼of that of the high-speed rate signal is placed next to signal 131, andsignal 133 with a rate ⅛ of that of the high-speed rate signal is placednext to signal 132. Thus, at the position of the spectral peak of eachtransmission rate is the null point of another spectrum. Therefore,placing signals as shown above does not affect transmission. As aresult, it is possible to transmit extra information corresponding to2.75 sub-carriers of the high-speed rate signal.

Furthermore, since a low-rate signal has a time diversity effect andhigh quality, an effect corresponding to 2.75 or more sub-carriers canbe expected by assigning a signal with-high quality requirements amonginformation to be transmitted such as the most significant bit of avoice signal and control signal to the position of the low-rate signal.

(Embodiment 2)

The data transmission apparatus according to Embodiment 2 of the presentinvention carries out the processing in Embodiment 1 above, andfurthermore processing of inserting guard intervals.

FIG. 11 is a functional block diagram showing the configuration of thedata transmission apparatus according to Embodiment 2 of the presentinvention. The data transmission apparatus in present Embodiment 2comprises high-speed mapping block 102 that maps part of transmissiondata 101 by means of high-speed mapping 1, low-speed mapping block 103that maps the rest of transmission data 101 by means of low-speedmapping 2, serial/parallel conversion block 104 thatserial/parallel-converts the transmission data mapped by high-speedmapping 1, inverse Fourier transformation block 105, and parallel/serialconversion block 106. Furthermore, the data transmission apparatus alsocomprises guard interval insertion block 109 that inserts guardintervals into a parallel/serial-converted time-series signal. Itfurther comprises quadrature modulation block 107 and transmissionantenna 108. In FIG. 11 there is a division into mappings with 2 kindsof speed, however it may be divided into any number of types.

The operation of the data transmission apparatus configured as shownabove is explained. Transmission data 101 is divided into a plurality ofportions by rate and mapped at different rates. The signal sent tohigh-speed mapping block 102 is mapped as high-speed symbol rate data bymeans of high-speed mapping 1. On the other hand, the signal sent tolow-speed mapping block 103 is mapped as low-speed symbol rate data bylow-speed mapping 2. For example, the low-speed symbol rate is set to ½of the high-speed rate. The signal subjected to high-speed mapping isserial/parallel-converted by serial/parallel conversion block 104,subjected to inverse Fourier transformation (IFFT) in inverse Fouriertransformation block 105 together with the low-speed mapped signal,parallel/serial-converted by parallel/serial conversion block 106 to atime-series signal. This time-series signal, with guard intervalsinserted by guard interval insertion block 109, is quadrature-modulatedby quadrature modulation block 107 to a radio frequency and transmittedfrom transmission antenna 108.

As described above, when carrying out multi-carrier transmission ofsymbols with different rates, a low-speed rate signal with a rate ½ ofthe high-speed rate, for example, remains the same over 2 symbols, butit may lose the phase continuity at a stage at which guard intervals areinserted. Thus, guard interval insertion block 109 needs to adjust thephase so that it may be continuous at the stage of insertion of guardintervals in guard interval insertion block 109.

In Embodiment 2, the phase that changes at guard intervals is calculatedbased on the relationship between the length of the guard interval andsub-carrier frequency beforehand, and low-speed mapping block 103carries out mapping by taking account of the calculated phase changeportion. This allows the spread of the spectrum to be suppressed despitethe presence of guard intervals.

Furthermore, Embodiment 2 is intended to improve the frequencyutilization efficiency by assigning a low--rate signal to the guardfrequency parts set at both ends of the band to which a plurality ofsub-carriers were assigned.

FIG. 12 is the spectrum of a single carrier. The result of insertingguard intervals is as shown with solid line 140, which is narrower thanoriginal spectrum 141.

As with Embodiment 1, placing low-speed signals at both ends of ahigh-speed rate signal makes it possible to transmit signals effectivelywhile maintaining an orthogonal relationship. In FIG. 13, placing signal151 with a rate ½ of the high-speed rate at the positions of 2 carriersnext to signal 150, placing signal 152 with a rate ¼ of the high-speedrate next to signal 151, and placing signal 153 with a rate ⅛ of thehigh-speed rate next to signal 152 will make it possible to effectivelyutilize the areas that have not been available so far. This allows extrainformation corresponding to 2.75 sub-carriers of a high-speed ratesignal to be transmitted.

Furthermore, since a low-rate signal has a time diversity effect andhigh quality, an effect corresponding to 2.75 or more sub-carriers canbe expected by assigning a signal with high quality requirements amonginformation to be transmitted such as the most significant bit of avoice signal and control signal to the position of a low-rate signal.

In FIG. 13, sub-carriers do not seem to be orthogonal to one another,but they become orthogonal to one another if the guard intervals areremoved, and thus they can be separated completely at the time ofdemodulation.

As described above, the present embodiment can introduce guard intervalsand thus it can improve the frequency utilization efficiency and realizetransmission resistant to multi-paths as well.

(Embodiment 3)

The data transmission apparatus in Embodiment 3 of the present inventioncarries out processing of Embodiment 2 above and further carries outprocessing of band restrictions.

FIG. 14 is a functional block diagram showing the configuration of thedata transmission apparatus according to Embodiment 3 of the presentinvention. The data transmission apparatus in Embodiment 3 compriseshigh-speed mapping block 102 that maps part of transmission data 101 bymeans of high-speed mapping 1, low-speed mapping block 103 that maps therest of transmission data 101 by means of low-speed mapping 2,serial/parallel conversion block 104 that serial/parallel-converts thetransmission data mapped by means of high-speed mapping 1, inverseFourier transformation block 105, parallel/serial conversion block 106and guard interval insertion block 109. Furthermore, the datatransmission apparatus also comprises band restriction block 110 thatcarries out band restrictions after inserting guard intervals. Itfurther comprises quadrature modulation block 107 and transmissionantenna 108. In FIG. 14 there is a division into mappings with 2 typesof speed, however it may be divided into any number of types.

The operation of the data transmission apparatus configured as shownabove is explained. A part of transmission data 101 is input tohigh-speed mapping block 102 and another part is sent to low-speedmapping block 103. The signal sent to high-speed mapping block 102 ismapped as high-speed symbol rate data by means of high-speed mapping 1.On the other hand, the signal sent to low-speed mapping block 103 ismapped as low-speed symbol rate data by means of low-speed mapping 2.For example, the low-speed rate is set to ½ of the high-speed rate. Thesignal subjected to high-speed mapping is serial/parallel-converted byserial/parallel conversion block 104, subjected to inverse Fouriertransformation in inverse Fourier transformation block 105 together withthe low-speed mapped signal. These signals are parallel/serial-convertedby parallel/serial conversion block 106 to a time-series signal, andguard intervals are inserted into it by guard interval insertion block109. This time-series signal is subjected to band restrictions in bandrestriction block 110 and quadrature-modulated by quadrature modulationblock 107 to a radio frequency and transmitted from transmission antenna108.

At this time, a signal with a rate ½ of the high-speed rate for example,remains the same over 2 symbols. Thus, in low-speed mapping block 103,the phase that changes at guard intervals is calculated beforehand basedon the relationship between the length of the guard interval andsub-carrier frequency and mapping is carried out by taking account ofthe changing phase. Mapping is carried out in this way so that the phasemay be continuous at a stage at which guard interval insertion block 109has inserted guard intervals. This makes it possible to suppress thespread of the spectrum even with the presence of guard intervals.

Furthermore, by applying band restrictions through band restrictionblock 110 unnecessary low-level signals that can be removed easilythrough a simple filter and a filter with a short impulse response areremoved through filters. At this time, a low-speed rate signal is placedin an area where there are signals which are difficult to be removed.This can reduce load on the filter, secures the frequency utilizationefficiency and time utilization efficiency simultaneously.

The data transmission apparatus in the embodiment above is used in amobile radio communication system. For example, suppose the above datatransmission apparatuses are incorporated in a mobile station and basestation and data transmission is carried out between the mobile stationand base station according to the OFDM system explained in the aboveembodiment. Especially, it is effective when using a band by dividing itfor each user on the uplink.

As described in detail above, the present invention can improve thefrequency utilization efficiency at both ends of the OFDM band.Furthermore, since guard intervals can also be introduced, it alsobecomes resistant to multi-paths. In addition, it can secure thefrequency utilization efficiency and time utilization efficiencysimultaneously by introducing band restrictions.

Industrial Applicability

The multi-carrier transmission method and the data transmissionapparatus that implements the method are useful in a radio communicationsystem.

What is claimed is:
 1. A multi-carrier transmission method, comprising:assigning high-rate data to a plurality of first sub-carriers,orthogonal to one another, set on a specific frequency band; assigninglow-rate data to second sub-carriers, orthogonal to the firstsub-carriers, set on guard frequency bands on both sides of the specificfrequency band; and concurrently transmitting the high-rate data and thelow-rate data.
 2. The multi-carrier transmission method according toclaim 1, wherein a transmission rate of the low-rate data is ½^(n) atransmission rate of the high-rate data.
 3. The multi-carriertransmission method according to claim 1, wherein data requiring highquality among transmission data is assigned to the second sub-carriersas the low-rate data.
 4. The multi-carrier transmission method accordingto claim 1, wherein the low-rate data is subjected to mapping inassociation with a phase variation at a guard interval, so that a phaseof multi-carrier signal is continuous at the guard interval.
 5. A datatransmitting apparatus comprising: a mapping system that carries outhigh-rate mapping and low-rate mapping with different rates; an assignorthat assigns first data subjected to the high-rate mapping to aplurality of first sub-carriers, orthogonal to one another, set on aspecific frequency band, and further assigns second data subjected tothe low-rate mapping to second sub-carriers, the second sub-carriersbeing orthogonal to the first sub-carriers and set on guard frequencybands on both sides of the specific frequency band; and a transmitterthat transmits the multi-carrier signal including the first data and thesecond data assigned by the assignor.
 6. A mobile station apparatuscomprising the data transmitting apparatus according to claim
 5. 7. Abase station apparatus comprising the data transmitting apparatusaccording to claim
 5. 8. An OFDM transmitting apparatus comprising: amapping system that performs mapping on transmission data; an IFFTsystem that performs inverse Fast Fourier transform on the transmissiondata input in parallel from the mapping system; and a transmitter thattransmits an OFDM signal output from the IFFT system, wherein themapping system carries out high-rate mapping and low-rate mapping withdifferent rates, the IFFT system assigns first data subjected to thehigh-rate mapping to a plurality of first sub-carriers, orthogonal toone another, set on a specific frequency band, while assigning seconddata subjected to the low-rate mapping to second sub-carriers, thesecond subcarriers being orthogonal to the first sub-carriers and set onguard frequency bands on both sides of the specific frequency band, toperform inverse Fast Fourier transform, and the transmitter transmitsthe OFDM signal including the first data and the second data.
 9. Amobile station apparatus comprising the OFDM transmitting apparatusaccording to claim
 8. 10. A base station apparatus comprising the OFDMtransmitting apparatus according to claim 8.